Salt-inducible Kinase (SIK)

Salt-inducible kinases (SIKs) belong to AMP-activated protein kinase (AMPK) family, and functions mainly involve in regulating energy response-related physiological processes, such as gluconeogenesis and lipid metabolism. The SIK family comprises three isoforms, namely, SIK1, SIK2, and SIK3, all of which may act as metabolic transmitters. SIKs have shown self-phosphorylation, and play an important role in regulating adrenocortical function under the stimulation of high salt or adreno-cortico-tropic-hormone (ACTH).

All three SIK family kinases are expressed broadly. SIK1 mRNA expression is regulated by multiple stimuli, including high dietary salt intake, ACTH signaling, glucagon signaling, excitable cell depolarization, and circadian rhythms. In contrast, SIK2 and SIK3 expression is constitutive in tissues in which these kinases are expressed. In humans, SIK2 and SIK3 are expressed ubiquitously, with highest SIK2 levels in adipose tissue and highest SIK3 expression in brain. In addition, these SIK family members are dysregulated in various cancers, including ovarian, breast, prostate, and lung cancers, indicating that SIKs may execute crucial roles in tumor occurrence or progression.